1. Technical Field
The present invention relates to a distortion identification apparatus, a test system, a recording medium, and a distortion identification method.
2. Related Art
A semiconductor test apparatus measures several types of characteristics of a semiconductor device under test (DUT). For example, a semiconductor test apparatus may input to a semiconductor device a test signal generated by an arbitrary waveform generator (AWG). In this case, the measurement is performed after a waveform digitizer performs a high-speed and highly accurate digital conversion on the signal output from the semiconductor device. In this way, the semiconductor test apparatus can test whether the semiconductor device is operating properly.
Japanese Patent Application Publication No. 7-209354 and Japanese Patent Application Publication No. 3-296308 are related prior art documents.
The arbitrary waveform generator and the waveform digitizer include analog circuits that transmit analog signals. An ideal analog circuit outputs an analog signal having a prescribed frequency corresponding to the input signal. In practical application, however, the analog circuit outputs an analog signal that includes harmonic wave components caused by the non-linear characteristics of the elements in the analog circuit. As a result, waveform distortion occurs in the output signal.
By inputting a signal having a single frequency and no distortion into the analog circuit and calculating the difference between the input signal and the signal output by the analog circuit to identify the distortion, a distortion signal can be acquired that indicates the distortion caused by the analog signal. In other words, the non-linear distortion caused by the analog circuit can be compensated for if the acquired distortion signal is subtracted from the signal output by the analog circuit.
In order to compensate for non-linear distortion caused by a signal that includes a plurality of signals at different frequencies, it is necessary to perform the identification using a multitude of single frequencies. When the number of frequencies being identified increases, a longer time is needed for the identification. Furthermore, since it is necessary to hold compensation information for each frequency, the amount of memory increases.